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MAY 1984

FINISHING TIPS

I have been getting a lot of questions about how to prepare and finish aircraft. I've talked to several other BD builders to get their ideas and methods and now will try to put it all together.

The most important part of finishing is getting the fuselage ready for painting. Never forget that paint will NOT cover any imperfection and make it look better. This includes sanding scratches, rivets, pin holes in fiberglass (oh yes they are there, you just can't see them), silicon rubber sealant, etc. I personally think that one of the largest mistakes made in trying to get a super finish is trying to fill too much. I'm referring to trying to feather a skin overlap back to about six inches. Very little drag comes from these edges whether they face the airstream or are the other way. The boundry layer along the fuselage is deep enough that these edges will never be noticed. These edges look best if the last quarter inch is bent down at a very slight angle. A bending brake of some sort is almost a must for this task because when doing it by hand over the edge of your workbench it is very easy to stretch the metal a little. This causes the metal to stand up some when you rivet it in place and ruins the whole effort. If the skin does not want to lay right, push a little pro-seal under the edge and hold or tape down until set (at least 24 hours depending on temperature). To seal the crack between the skin edge and the skin it overlays so that paint will not appear cracked, I used a thick, mixture of the poly urethane primer to be used on the airplane. I mixed in the catalyst and let it set until most of the carrier evaporated out and the mixture became thick. I used a small paint brush to fill the crack but did not try to make the edge disappear. After drying for a day or two, it was sanded with 400 grit wet sandpaper. I had to refill in a couple of places and sand again later. This technique was used on all skin edges on the airplane and I can't think of any that have broken loose and cracked the paint (all skins on my airplane are bonded with 3M 2216 - it is not bad but I should have used Pro-Seal).

Other builders said they used Bond-O (quite heavy) or Ultra-lite (same as BondO but has microballoons in it) to fill dents and edges. These fillers work very well as they set up quickly and are easy to sand. The drawbacks are that they are not flexible enough and sometimes a crack will occur later, and they have to be prepared before painting. They must be cleaned with MEK or acetone to remove the wax used to aid in curing. If they are not cleaned well enough, the paint will separate from all wax spots and you will probably get a run trying to cover them. Be sure to prime over all such filler and sand and reprime until you get it right. It is a real mess trying to deal with it on the day you planned to paint the whole airplane.

For those of you who want to fill your countersunk rivets, the accepted procedure is to dip the rivets in primer before you set them, then fill the holes with something later. DO NOT use silicon material as paint will not stick to it and it's very hard to clean up enough to do something else. I took a plastic disposable hypodermic shringe, pulled the needle out of it's metal housing and then drilled the housing to the size I needed. It is kind of messy to fill the hypodermic but it sure is neat to poke it in the hole and fill. As to what to use. I used 2216 but ProSeal or the Bondo products will work as well. After the filler sets it should be sanded and then filled with thick primer and wet sanded again until smooth. Fred Hinsch asked about using glazing putty to fill edges and rivets. I think it will work fine as long as it is compatable with the paint you will be using.

The choice of primer should be made so that it is compatable with the finish coat. Only a thin layer of primer is needed. If there are a lot of areas that the primer does not cover well (fill, etc,), and you have to rework and respray (especially if this takes several days) the surface should be lightly sanded before the finish coat. Some shops rub the surface with brown grocery bags instead of sand paper as the primer coat is very fragile and can easily be sanded through.
The finish coat of paint should be sprayed on quickly so that the over spray won't have as much an effect. The bottom should be sprayed first, the sides second, and the top last so that any overspray there will be dissolved in the fresh paint. It is always a good idea to limit how much you have to paint in a day. Do the wings, stabilator, fuselage, cowling, miscellaneous fairings, etc., separately. You do not realize how much surface area an airplane has until you try to paint it in one day. The choice of paint has a large effect on how hard it is to paint your airplane. Some paint colors cover very well and only a thin layer is needed. This is really best as it also reduces the weight of the paint. Remember, paint can have a substantial effect on your weight and balance. If you want your airplane basically white as most of us do, use an off white as it covers much better. I used a very pure white and had 6 to 8 thin coats to get it to cover the pale yellow primer. The more coats you put on, the rougher the final finish. Some paints like laquer, enamel, and modified poly-urethanes can be rubbed out and so you can get rid of the roughness. Pure poly-urethanes cannot be rubbed out or patched and are much harder to get right. They have a beautiful "wet" look but can be a bit of trouble. If many coats are to be used the surface should be lightly sanded before the final coat. The amount of paint needed for a BD-4 is very difficult to guess because of the reasons stated above. I must have gone through at least 6 gallons of finish coat. There really is no reason for this as a color with better covering characteristics should have been used.
For masking off your airplane, the old standby masking tape works ok but the 3M-Scotch Fine Line tape is substantially better. It goes around curves beautifully, can be pressed down much easier (you can see through it and tell where it is not pressed enough). It will give you a very fine line when you pull it off shortly after painting. It is light green in color and is sold in most auto paint stores.

ENGINE BAFFLES

Those of you who have tried to "baffle" an engine know what a problem it is. Engines are not designed with air baffling in mind. An air cooled engine requires that air not only be forced around the engine but through the fins on the heads. A Lycoming O-360 type engine requires a certain differential pressure between the incoming air plenum and the other side of the engine (either up draft or down draft can be used). An IO-360 has fins that are more numerous, larger and requires more pressure differential yet (more horsepower - more cooling required). It is important to set up the air flow so that hot spots are avoided. Hot spots on the heads can cause warping, cracking, and very large repair bills.

The BD-4 plans show a common method of baffling that will work but is a lot of work to install and maintain. It also does not allow for a smooth expansion (and slowing) of the air as it flows into the engine compartment. On both the BD's I have built we have had over heating problems. A new cowling with larger inlet holes helped some but not really enough - the BD nose bowl holes are really large enough - the problem lies elsewhere.

A lot of air can escape past the rubberized asbestos baffle seals. It is hard to get these seals to lay flat against the cowling and because the engine moves around a lot, some can open up and spill a lot of air. The seals are several feet long so generally a lot of leak occurs. Remember that as the prop turns clockwise, the engine torques counter-clockwise. This usually causes the right side baffles to hit the cowling and make a lot of noise, and the left side baffles to unseal and spill air. Any air that spills, lowers the pressure differential and ruins the whole plan. Using the cowling as a part of the pressure plenum causes the cowling to change shape (lift) which can also let air escape over the baffles.
Another aspect of airflow through your engine fins is what the pressure is below your engine - you must have a good air outlet. This means the air should come out in the same direction as the air is normally flowing along the fuselage (is. not squirting straight down out of the engine compartment). Also, it should exit into a low pressure area. Both of these "musts" are violated by the cooling system on the BD-4.

The 90 degree angle the firewall forms with the bottom skin makes it very hard for the air to turn the corner and join with the air flowing under the aircraft. This causes a disruption of the airflow which is a drag increase. If the cooling air is directed out correctly, some thrust can be obtained. The F-51 Mustang recovers many horsepower due to the expanded (heated) air blowing out of the rear of the radiator compartment. I don't know if we could get any thrust but it helps to make the air flow out smoothly. A fairing such as shown in figure I helps a lot.

In figure 2 an added advantage from the figure 1 fairing is shown. In steep climb attitudes the relative wind causes air to ram into the outlet and cause higher pressure below the engine and so less pressure differential. The fairing helps eliminate this.
The outlet location is not ideal as it is a high pressure area. The ideal place to outlet air is just behind the spinner on top of the cowling like the Rutan Defiant and others. However, the most convenient place to have the outlet without doing an awful lot of work is right where it is now so lets look further for a solution.

Cowl flaps help control temperatures because when they are down (open), they deflect the airstream and cause a low pressure area behind them which allows the air in the cowling to get out easier. Cowl flaps are almost considered a must on high performance aircraft but I personally hate them. They cause a lot of drag when they are open, are easy to forget to use, and are a lot of trouble to build and maintain. So far I haven't needed them for keeping the proper temperature up at altitude as my airplane always runs just right at altitude. I make powered desents to keep the engine from shock cooling. If I improve my baffles a lot, I might have to build a variable outlet hole - but it won't be the common tip down variety. It might work to adjust the fairing in figure 1 so that the size of the opening is reduced.

Many people have recommended "racing" baffles to me. I've recommended this method to a couple of builders in this area (you know let them try it first and if it doesn't blow up - I'll try it). Glenn Dickenson, Dave Dotson, and Duane Roberts all use it and have excellent cooling. The racing baffling consists of a plenum chamber over each side of the engine (2 cylinders under each). The plenum is totally enclosed (except for the bottom) and fits up close to the cowling air inlet. The rubberized asbestos gasket closes the 1/2 inch gap between cowl and baffle. This greatly reduces the length of gasketing and makes it much easier to seal for leaks. The top of each plenum hinges open for spark plug maintenance.

As this method seems to work and my BD style baffles were really ragged, I am now installing racing baffles on my BD-4. Most of the baffle is just a modification of the BD style.  Metal (I like to use 2024-0 aluminum of about 0.040 thickness) is fit around the valve covers as usual and metal is fit across rear cylinders (wraps partially around the bottom). I then made a piece that fits over the area where the push rods go into the center case and then a top for the box. The most difficult part is doing the metal work to get the air up from the air inlet and to the plenum. Metal was tried but is very difficult for such a strange shape. I made the air "duct" from fiber glass as it gets along well with strange shapes. I used foam, wood, tape, and metal to mock up what I wanted and covered the inside with glass. This is very difficult as part of the time you are working through the air inlet hole. The right side "duct" will supply air for cylinder cooling, cabin heat, cabin cooling, and alternator cooling. The left "duct" supplies cylinder cooling and has a built-in air cleaner/carburetor air "funnel". The oil cooler is bolted on the back of the left baffle as usual (my hoses are not long enough for anything else). I've been told by experts that the air needed for everything should be taken off of the baffles rather than separate scoops, NASA vents, etc. This makes for fewer rain leaks, drag, and complexity. Be sure to insulate the cabin fresh air hose so it doesn't pick up any heat.

The dual separate plenums could cause one side to be cooled more than the other. I intend to use an old airspeed indicator to check the pressure differential of each of the plenums. The static port is connected to a tube that goes under the engine and the pitot connection is connected in turn to tubes that go to each of the plenums. The resulting airspeed is a measure of pressure differential. If one side is cooled more than the other maybe I'll have to close off part of one inlet, or put in a cross feed pressure equilizer.

I hope that all this work will cut my cooling drag and so help my CAFE 400 score. I am making drawings of each metal part and am making a mold of the fiber glass "ducts" so maybe someone else can use them. I`11 let you know more after some test flight.

Figure 1
Click on image for larger view

VISION PROBLEMS

Ever heard of a Radial Keratotomy? If you have myopia (near sightedness) maybe you should look into it. A year or so ago I went for my FAA physical and asked for a second class. I don't know why - I have my Commercial rating but never use it. I had passed the second class medical once before as they forgot to check my eyes. This time they caught it, refused me the second class and told me to try for a waiver. I've been told that there is a regulation even requiring private pilots to carry a second pair of glasses if their vision is bad. I suppose it's a good idea even if it is not a law. I had recently heard about the Radial Keratotomy and started to look into it. Anyone who has bad eyes (can't see the big E) will grasp at any straw which might solve the problem. It is embarrassing to see someone waving on the other side of the swimming pool and not be able to tell if it is friend or foe. In the military during hand to hand combat training we had to take our glasses off so they wouldn't get broken. I couldn't see that the Drill Instructor was watching me and laughed at an inopportune time (I hate 20,000 squat thrusts!).

This procedure was discovered in the Soviet Union in the early 1970's when a school boy had the cornea of his eye cut in a radial pattern when his glasses were shattered. As the cornea healed (a day or two) his vision got much better. His doctor theorized that the scar tissue formed around the edge of the "bump" allowed a change in the shape of the "bump" on the front of the eye. This "bump" is responsible for about 70 percent of the focusing - the rest being done by the lens. After first experimenting on animals he began operating on humans in 1974.

The cornea is cut to 50 to 75 percent of its depth and in a radial pattern that looks like the spokes of a wheel. The central area is not cut. The number of radial cuts varies from 4 to 24 depending on correction needed. A 4 diopter correction requires at least 8 cuts. The cuts are done by hand (with microscopic aid) with a depth controlled scalpel. The operation is done in the doctors office and takes about 10 minutes. The patient is awake and with only the standard numbing drops in the eye. The hardest part of the operation is looking into the bright microscope light. You can see the scalpel cut your eye and a blurring of the light occurs as the scalpel pushes your eye out of shape.

In most cases vision improves to 20 - 20 within two hours. Your eye tears quite a bit but it's fantastic to see that trees a block away actually have individual branches! Recovery time and pain encountered depend on the number of cuts needed. The cornea knits together in about 12 hours after which the pain is minimal. The eye continues to tear and vision varies from morning to night and day to day. During the mornings of the first week the swelling that occurs during sleep makes the focus very different and your brain will not be able to focus both eyes at the same time (only one is operated on at a time). I had a little trouble with driving - mostly because of the tears running down my cheek and also light sensitivity. After 10 days there is no pain and only slight tearing. Vision tends to be far sighted (20-10 or 20-5) at two days and then varies depending on time of day until at 10 weeks when they stabilize. Vision might not be 20-20 but can be easily touched up with small cuts, very little pain and 1 day recovery time. I had my right eye re-adjusted last Friday and had 4 cuts, one for astigmatism and 3 for myopia. I took a codiene tablet and went to sleep on the couch for about 6 hours after which I felt fine. The next day I worked 10 hours on the airplane and had no discomfort. My eyes are very close to 20-20 now with only a little astigmatism left. It is harder to correct for astigmatism. It requires a concentric cut along one side of your eye to "pull" the wrinkle out. A cut for astigmatism causes your eye to become more myopic, so some radial cuts are required to recorrect that.

The price? Well, about 3 months of varying vision problems and $2000 dollars. $1000 per eye for as many cuts and recuts as are needed. Some people don't correct as well as others but everyone seems to get pretty close to 20-20.

Now that I can see, I feel so good it makes me want to go get a "high paid" job as an airline pilot - something that has always been denied me.

CAFE 400

The CAFE 400 is to be held at Santa Rosa, CA an June 22 and 23 (at the Santa Rosa Air Center Airport). the course will be flown counter-clockwise this year, otherwise there are no changes. Information sheet is $5.00 (payable to CAFE Foundation) from CAFE Inc., 4305 Leafwood Circle W., Santa Rosa, CA 95405.  Get your entry in quick - I'm already signed up. It has been a busy year so the only improvements I'm making are to the baffles and a new Ellison carburetor (Sport Aviation, March 1984). I will also try to aviod all the mistakes I made last year. For those of you who don't want to race but live close enough - come watch. The race itself is on Saturday and usually somebody needs bodies to ride along to get to gross weight. If you want a ride you should be there by noon on Friday for weigh-in.

ELLISON CARBURETOR

Ray Ward called me before I even got my March Sport Aviation to let me know about the Ellison Carburetor covered therein. Supposedly, this carburetor should allow me to save a gallon of gas per hour at cruise power as it allows you to lean a lot further before extreme roughness occurs. This was a problem on the last CAFE 400. I was running about 2000 rpm and higher manifold pressure for economy. I can lean my engine very nicely at higher rpm but at 2000 one of the cylinders gets lean way before the others. This supposedly is caused by unequal distribution of gas to the cylinders. The Ellison does not have a butterfly and is reputed to have better distribution. I have made an arrangement to get one to test and use for the race if I like it. It is kind of handy as the Ellison brothers are going to set up shop in Renton, WA which is about 10 miles from my home. I will be doing some tests soon and will write about it later.

One of the nice things about the Ellison is that it has a much lower profile than the Marvel-Schebler MA-4-5 that most of us are using. The Ellison EFS-4-5 is a direct replacement but is shorter and has a larger effective venturi. If you need more room , the EFS-4 has the same effective venturi but it is shorter yet. This looks like an ideal way to get a correctly shaped carburetor air box and also get it to fit within a normal BD-4 cowling.

WHEN TO CALL

I still work for the Boeing Military Airplane Company and can take short calls during the day. I work from 8:00 to 3:30 Pacific time with my lunch from 11:30 to 12:30. Lunch time would be an excellent time to call as I usually stay at my desk. The new number is 206-394-3421. You can also call my home, evenings, 206-631-5324.

LETTERS

William Singer needs the hose clamps that fasten the panels to the spars. If you have some or know where to get same, 816-565-2558.

Harry Crawford would like to see some drawings and "how to" information for Jost Wallimans top hinged doors. Send to me and I will put them in the next newsletter.

Don Hastings needs BD-4 plans and/or handbook (see new address).

Pill DeProsse (BD-4 amphibian - see newsletter # 9) has had some gear problems during taxi tests and is now reworking some things including some damage to the fiber glass hull (says his wife is learning a lot about fiberglass). He should fly in about 2 months.  Bill says he also needs a center section spar for another BD-4 that he has.  415-827-0199

John Stewart. Eugene, OR bought Herb Talen's BD-4 and is keeping it flying while he reworks it little by little.

Larry Lux. Russel Kilpatrick, and many others are having trouble with leaky wing tanks. Once they start to leak (especially the inboard rib) it is impossible to get them to quit. They almost never leak fast, but tend to seep forever. I've noticed that everyone who tries to fix a leak seems to open the top of the wing panel. The seep problem seems to be almost exclusively just below the spar on the inboard rib. I have tried to clean and reseal the inboard rib from the top and know that it just can't be done. There is no way to get under the spar and clean out the 10 layers of slosh, etc. We have a new BD-4 owner here in the Seattle area and we are going to try opening the panel from the bottom. This should allow us to work the problem much better. The only problem is resealing the tank. We think we have a good idea for that too. We will tell you about. it later after it works?

John Brecher has Cleveland wheels and BD main gear legs for sale. 816-637-1004.

Wayne Johnson says he has a 2 : 1 trim reduction method - could we get some drawings?

Dick Bushman has a complete cabin yoke assembly for sale (including rudder cable pulleys). 206-636-2135

Ray Ward can't find enough to do. He had a little problem with mud in his wheel pants awhile back and while repairing the front of his BD-4 decided to make some changes. He extended his ram air tube to within 2 inches of the prop and also changed his cowling inlets to 5 X 4.75 and made 2 inch radius edges. He is very happy with a 4 mph increase in speed at 24/24. Ray did some performance checks to see if he could enter the LBF 500 and found that 190 mph is very hard to get with out running out of fuel (a-ha just what I suspected). We know the Mooney can't do it - sure would be nice to find a BD-4 that could. Ray likes the idea of a turbo wankel for his BD-4. Dan Duncan is jigging up to make BD-4 engine mounts for the wankel. Would you believe 240 HP normally aspirated ($6700) or 350 HP turbo. They use a 3:1 reduction cog belt drive. 3000 hours TBO and only weigh 250 lbs? He expects to enter a 275 mph wankel powered BD-5 in the Oshkosh LBF 500 this year.

Dan Duncan thinks I should put aft facing rear "club seats" in my BD-4 so I can meet the seat width requirements for the LBF.

John Schippers wrote to let us know he made it home OK after Oshkosh. John lost a propeller in Iowa but still came to Oshkosh to tell us about it. He just bought a used pickup truck and trucked it home (Stockton, CA). John is now looking for an idea that will make it easier to push around a taildragger. Something that will attach to the back-end somehow.

Fred Hinsch wrote to tell us he is about ready to fly. He purchased a Murphy wing and found it to weigh 107.5 lbs total of all the parts.

Several builders wrote to help me with questions on using spark advance when running lean. Harry Crawford sent some information on "in cab spark adjustment". This looks good but you would have to do some re-work on your mags - too bad I'm not running a converted auto engine as that would make it easier.

Gene Stearns wrote and told me about the methods used on the Boeing 850 which used 4360's. They had the advantage of torque meters and ignition analyzer scopes. They could get as lean as 0.055:1 fuel/air mixture. 'the normal advance was about 20 degrees but could get 30 degrees at best.

Jim McCord sent information about Bob Porter of Sacramento who modified his cessna turbo 210 to include an in cockpit spark, advance. When running 40 to 50 degrees lean of peak he can advance 6 to 10 degrees. He puts a second set of points in a "Shower of Sparks" type of magneto and uses relays to activate them after leaning.

I really appreciate all the letters on this and other subjects. I still need articles for the newsletter - I know a lot of you have a lot to say but it is hard to sit down and write.

Ernest Lanyi sent a history of the things he has done on and with his BD-4. He has so many airplanes, I don't see how he gets anything done. He has a Cherokee Warrior he repaired, started building a BD-5, is now building a Falco and also working on a 1981 Cessna Skyhawk. He first flew April 14, 1973 and has done some very different things with it. It has been approved by the FAA for intentional parachuting. He has dropped his two sons and daughter several times, simultaneously, and each of them separately many times. The FAA approved it for parachuting only after it was demonstrated that it could fly safely with the door off. Ernest believes his BD-4 was the first modern, homebuilt to be FAA approved for parachuting.

BAYVIEW (ARLINGTON) FLY-IN REPORT

The Arlington Washington fly-in was held a few miles away at Bayview this last year. Politics caused the move and now politics have caused a move back to Arlington for 84.

Last year we had a very good turn out of airplanes and BD-4's in particular. The builders with airplanes present were : Del Kendrick, Colin Powers, Dave Dotson, Glenn Dickenson, and Roger Mellema. Duane Roberts was working on his and just missed the fly-in. Other builders present were Dick Gushman, Jim Parker, Bill VanNoy, Fred Hinsch, and Eric Munzer.

Aside from some overzealous fly-in "officials" who wanted to throw their weight around, we had a good time talking about BD-4's and looking at all the other airplanes. There was no allowance for a fly-by pattern but we went up anyway and did one. Colin Powers led the pack with Del Kendrick flying formation close by. I don't think Colin could have lost Del even if he tried. Del is an ex-military pilot and flys formation beautifully. Dave Dotson and I followed after Del and did the best we could (we need more practice). As we flew by, we were within a block of so of the leaders. No matter how it looked, we sure had fun. This year at Arlington there will be an official fly-by pattern - they finally reacted to all my bitching. Now if someone would just run over the ding-dong they had in charge of aircraft parking.

We hope everyone in the area can make Arlington 84. This year we have no charge for entry or camping to the pilots and passengers who fly in. There is plenty of parking space and space to pitch your tent. Food of many types can be purchased. The fly-in has been scheduled for August 11 and 12 which is the same weekend as the Abbotsford, BC airshow. Make a weekend of it and see both shows. There will be a welcome-back chili feed for EAA members on the evening of August 10 (some people arrive on Wednesday already). A temporary FAA flight information tower will be in operation on Aug 11 and 12.

NEWSLETTER DUES

Thanks to all of you who sent in your dues since the last issue. Many of you had received 3 free issues already and the coffers were running a little low. Please check for the * in front of your name. If it is not there, you won`t get any more newsletters. If you want to continue getting them, the price is $ 5.00. I found a new cheap printer which will help streach the money.

NEW NAMES AND ADDRESSES

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